Impact of tidal energy converter (TEC) arrays on the dynamics of headland sand banks

Previous results from one-dimensional model studies have demonstrated that large-scale exploitation of the tidal stream resource could have a significant impact on large-scale sediment dynamics. In this research, we model the impact that such exploitation would have on the dynamics of headland sand banks. Such sand banks, formed by the large eddies generated by strong tidal flow past headlands, have an important role in natural coastal protection, since they cause waves to refract and dissipate energy. Therefore, a tidal energy converter (TEC) array developed in the vicinity of a headland could alter this natural form of coastal protection. Here, we investigate the impact of TEC array operation on idealised headland sand bank formation, followed by a case study, the Alderney Race: a strait of water between the island of Alderney (Channel Islands) and Cap de la Hague (France). This is achieved through the application of a morphological model that incorporates TEC device operation as an additional bed friction source term in the three-dimensional hydrodynamic module. Through a series of model experiments, we demonstrate the impact that a full-scale (300 MW) TEC array would have on sediment dynamics when sited near a headland. This modelling study demonstrates that a 300 MW TEC array located in the vicinity of a headland could lead to a considerable change in the maintenance of headland sand banks over a spring-neap cycle. If the scale of this change is demonstrated to be significant compared to the natural range of inter-annual and inter-seasonal sand bank variability, then developers of TEC arrays would be advised to examine ways in which they could reduce the environmental impacts of TEC arrays sited near headlands. The most obvious of these is to limit the scale of the array, but if we assume that developers wish to exploit the tidal energy resource to its maximum, the alternative is to site the array strategically (within the bounds of economic feasibility) such that it will not interfere with the natural morphodynamics of the headland system.